Process for the preparation of 6-(arylcarbonyl)-4-oximo-dihydrobenzothiopyran herbicides and intermediates useful therein

ABSTRACT

The present invention provides compounds of formula I and processes for the preparation and purification thereof. ##STR1## Compounds of formula I are useful as intermediates in the manufacture of 6-(arylcarbonyl)-4-oximino-dihydrobenzothiopyran herbicidal agents.

Provisional Application No. 60/098,829 filed Sep. 02, 1998 ProvisionalApplication No. 60/061,477 filed Oct. 08, 1997.

BACKGROUND OF THE INVENTION

Dihydrobenzothiopyran compounds (thiochromans) and4-oxo-dihydrobenzothiopyran compounds (thiochromanones) and the 4-oximeand 4-alkoxime derivatives thereof are useful intermediates in thepreparation of 6-(arylcarbonyl)thiochroman herbicidal agents. Saidherbicidal agents and methods for their preparation are described inU.S. Pat. Nos. 4,919,705; 5,468,722 and WO 95/13275. The6-(arylcarbonyl)thiochromans and derivatives thereof are effectiveherbicidal agents at low rates of application and demonstrate selectivecontrol of noxious weeds in the presence of key economic crops such ascorn and rice.

Heretofore, methods to prepare the above-said thiochroman andthiochromanone intermediates required appropriately substitutedthiophenol starting materials which may be commercially unavailable anddifficult to prepare. The importance of thiochroman and thiochromanonederivatives, particularly as essential intermediates in the manufactureof herbicidal 6-arylcarbonyl-thiochroman agents, creates a significantneed in the art for alternative and effective processes for theirmanufacture.

SUMMARY OF THE INVENTION

The present invention provides compounds of formula ##STR2## wherein R₁and R₂ are each independently C₁ -C₄ alkyl;

W₁ is --SCR₄ R₅ CR₆ R₇ COOH;

W₂ is H or W₁ and W₂ may together with the carbons to which they areattached form a ring in which W₁ and W₂ represent ##STR3## R₃, R₄, R₅,R₆ and R₇ are each independently H or C₁ -C₄ alkyl;

Z is O or NOR₈ ; and

R₈ is H, C₁ -C₄ alkyl or C₁ -C₄ haloalkyl; or

when Z is NOR₈, the stereoisomers thereof.

Also provided are a process to prepare a thioenol formula Ia compoundvia the condensation of Hagemann's ester and a β-mercaptopropionic acidand a process to prepare a tetrahydrobenzothiopyran formula Ib compoundby the cyclodehydration of the formula Ia thioenol. ##STR4##

Further provided is the use of the formula I compounds of the inventionas intermediates in the manufacture of herbicidal6-(pyrazol-4-yl)carbonyl-dihydrobenzothiopyran, 4-oxime and 4-alkoximecompounds and in the preparation of dihydrobenzothiopyran intermediatestherefor.

Still further provided is a process for the purification and isolationof compounds of formula Ib wherein Z is O.

DETAILED DESCRIPTION OF THE INVENTION

Preferred compounds of formula I are those compounds wherein R₃, R₄, R₅,R₆ and R₇ are H. Also preferred are compounds of formula I wherein R₁ ismethyl or ethyl. Further, compounds of formula Ib wherein Z is NOR₈ andR₈ is H or methyl are preferred.

The term haloalkyl as used in the specification and claims designates analkyl group C_(m) H_(2m+1) which may be substituted with 1 to 2m+1halogen atoms which may be the same or different. The term halogendesignates Cl, Br, I or F.

The compounds of the invention of formula Ib wherein Z is NOR₈, (Ib2)include the E and z stereoisomers shown below. ##STR5##

Compounds of the invention exemplary of formula Ia include: ethyl4-β-carboxyethylthio-2-methyl-1,3-cyclohexadiene-1-carboxylate; methyl4-p-carboxyethylthio-2-methyl-1,3-cyclohexadiene-1-carboxylate; ethyl4-β-carboxyethylthio-2-ethyl-1,3-cyclohexadiene-1-carboxylate; methyl4-β-carboxyethylthio-2-ethyl-1,3-cyclohexadiene-1-carboxylate; and thelike.

Compounds of the invention exemplary of formula Ib include: ethyl5-methyl-4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyran-6-carboxylate;ethyl5-methyl-4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyran-6-carboxylate,4-oxime; ethyl5-methyl-4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyran-6-carboxylate,4-(0-methyloxime); methyl5-methyl-4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyran-6-carboxylate;methyl5-methyl-4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyran-6-carboxylate,4-oxime; methyl5-methyl-4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyran-6-carboxylate,4-O-methyloxime; and the like.

Thiochroman (tetrahydrobenzothiopyran) and thiochromanone(4-oxo-tetrahydrobenzothiopyran) derivatives have heretofore beenprepared by the reaction of an appropriate thiophenol substrate with anα,β-unsaturated carboxylic acid, or a 3-halopropionate, followed bycyclodehydration. However, the required appropriate thiophenol startingmaterial may be unavailable commercially and can require up to foursynthetic steps to prepare.

It has now been found that thiochromanone derivatives may be preparedfrom the readily available Hagemann's ester of formula IV. The formulaIV ester may be purchased or, alternatively, may be prepared from theeasily obtainable simple starting materials of alkyl acetoacetate andformaldehyde.

Surprisingly, the formula IV ester may be condensed with aβ-mercaptopropionic acid of formula V to give the thioenol formula Iacompound of the invention. The reaction is shown in flow diagram Iwherein R₁ and R₂ are each independently C₁ -C₄ alkyl and R₃, R₄, R₅, R₆and R₇ are each independently H or C₁ -C₄ alkyl. ##STR6##

The condensation may be carried out in the presence of a solvent, anacid catalyst and the azeotropic removal of water. Suitable solvents areany inert solvent capable of forming an azeotrope with water such astoluene, benzene, halobenzene, xylene or the like, preferably toluene.Suitable acid catalysts include sulfuric acid, methanesulfonic acid,p-toluenesulfonic acid, pyridinium p-toluenesulfonate, borontrifluoride, pyridinium methanesulfonate and the like, preferablypyridinium methanesulfonate or pyridinium p-toluenesulfonate. Anyappropriate water separator, such as a Dean Stark trap may be used toremove, the azeotroped water. Increased reaction temperature leads toincreased reaction rate and drives the reaction to completion. However,excessively high temperatures may be detrimental and are not required.Preferable reaction temperatures may range from room temperature to thereflux temperature of the solvent, about 25°-200° C. more preferablyabout 75°-150° C.

Alternatively, the condensation illustrated in flow diagram I may becarried out in the presence of a solvent, an acid catalyst and adehydrating agent. Suitable dehydrating agents are acetic anhydride,triethyl orthoformate, trimethyl borate, and the like, and mixturesthereof. Solvents suitable for use include toluene, benzene,halobenzene, xylene and the like, preferably toluene. Acid catalystsuseful in the condensation include sulfuric acid, methanesulfonic acid,p-toluenesulfonic acid, pyridinium p-toluenesulfonate, borontrifluoride, pyridinium methanesulfonate and the like, preferablypyridinium methanesulfonate or pyridinium P-toluenesulfonate.

The formula Ia thioenol compounds of the invention may be readilyconverted to 4-oxo-tetrahydrobenzothiopyran compounds of formula Ib1 viaa simple single cyclodehydration step as shown in flow diagram IIwherein R₁, R₂, R₃, R₄, R₅, R₆ and R₇ are as described hereinabove.##STR7##

The cyclodehydration may be carried out in the presence of a solvent anda dehydrating agent and optionally in the presence of an acid catalyst.Solvents contemplated for use in the cyclodehydration reaction are anyinert solvent which is relatively nonreactive towards water or any ofthe utilized reagents. Suitable solvents are toluene, benzene,halobenzene, xylene and the like, preferably toluene. Dehydratingreagents particularly suitable for the cyclodehydration reaction shownin flow diagram II are acetic anhydride, trifluoroacetic anhydride,phthaloyl chloride, trifluoroacetyl chloride, and the like. Acidcatalysts which optionally may be present include sulfuric acid,methanesulfonic acid, p-toluenesulfonic acid, pyridiniump-toluenesulfonate, boron trifluoride, pyridinium methanesulfonate andthe like, preferably methanesulfonic acid. Reaction rate is increased byincreased temperatures, however excessively high temperatures may bedetrimental and are to be avoided. Suitable reaction temperatures mayrange from 0° C. to the boiling point of the solvent.

Advantageously, the cyclodehydration of a thioenol compound of formulaIa to form a 4-oxo-tetrahydrobenzothiopyran compound of formula Ib1 maybe performed in situ, thereby allowing the formation of said formula Ib1compound from a formula IV Hagemann's ester in a single reaction vessel,utilizing a common solvent system and acid catalyst.

Compounds of formula Ib1 thus-obtained are frequently tacky, gummysolids which may be very difficult to isolate and purify. Surprisingly,it has now been found that compounds of formula Ib1 may be crystallizedby treating said compounds with a solvent mixture of isopropanol andheptane, thus allowing ease of isolation via simple filtration andoptimal purity. A preferable solvent mixture is a mixture of about 1:1volume/volume isopropanol:heptane. Advantageously, the mother liquorsobtained from the filtration process may be recycled and usedcontinually to further isolate and purify the formula Ib1 compound.

Those compounds of the invention of formula Ib wherein Z is NOR₈ (Ib2)may be prepared by conventional oximation or alkoximation methods suchas reacting the formula Ib1 ketone with an oxylamine, H₂ NOR₈ or a saltthereof in the presence of a polar solvent and an acid acceptor. Thereaction is shown in flow diagram III wherein R₈ is H, C₁ -C₄ alkyl orC₁ -C₄ haloalkyl and R₁, R₂, R₃, R₄, R₅, R₆ and R₇ are describedhereinabove. ##STR8##

The oximation reaction may be accomplished in a polar solvent such as analiphatic alcohol, acetic acid, or the like, or combinations thereof, inthe presence of an acid acceptor such as pyridine, sodium acetate, orthe like. Reaction temperatures are directly proportional to reactionrate. Therefore, increased reaction temperatures lead toincreased-reaction rate. However, excessively high reaction temperaturesmay lead to decomposition and undesirable side reactions. Suitablereaction temperatures range from room temperature to the refluxtemperature of the solvent, i.e. about 25° C. to the boiling point ofthe solvent.

The present invention further provides the use of the compounds offormula I in a process to prepare important dihydrobenzothiopyranintermediates of formula III in the manufacture of6-(arylcarbonyl)thiochromanone herbicidal agents. Advantageously, theinventive process provides a route to the key formula IIIdihydrobenzothiopyran intermediates starting from the readily availableand easily obtainable Hagemann's ester compound of formula IV.

In accordance with the invention dihydrobenzothiopyran intermediatecompounds of formula III may be effectively prepared by condensing aformula IV ester with the appropriate β-mercaptopropionic acid offormula V to give a thioenol compound of formula Ia; cyclodehydratingsaid thioenol to give a 4-oxo-tetrahydrobenzothiopyran compound offormula Ib1; reacting said formula Ib1 compound with an oxylamine, H₂NOR₈, or a salt thereof to give the 4-oximino-tetrahydrobenzothiopyrancompound of formula Ib2; and aromatizing said formula Ib2 compound togive the desired formula III dihydrobenzothiopyran.

Optionally, the formula Ib1 compound may be aromatized to give a formulaVI 4-oxo-dihydrobenzothiopyran compound; and said formula VI compoundmay be reacted with an oxylamine, H₂ NOR₈, or a salt thereof to give thedesired formula III dihydrobenzothiopyran. The process of the inventionis shown in flow diagram IV wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇ and R₈are described hereinabove. ##STR9##

Aromatization of formula Ib1 to formula VI, or formula Ib2 to formulaIII, may be accomplished by a variety of oxidizing agents such asbromine, dichloro-dicyanoparabenzoquinone (DDQ), sulfur, or the like, inthe presence of a solvent such as methylene chloride, chloroform,toluene, acetic acid, or the like, or mixtures thereof. Alternatively,aromatization may be performed by using conventional dehydrogenationtechniques such as heating in the presence of a catalyst such aspalladium on carbon (Pd/C) and a solvent, optionally in the presence ofa hydrogen acceptor. Hydrogen acceptors include conventional hydrogenacceptors such as any olefin capable of reduction, e.g. maleic acid,cyclohexane, cyclohexadione and the like.

The compounds of formula III are useful as key intermediates in themanufacture of 6-[(pyrazol-4-yl)carbonyl]dihydrobenzothiopyranherbicidal agents of formula VII ##STR10## wherein R₂ and R₉ are eachindependently C₁ -C₄ alkyl;

R₃, R₄, R₅, R₆, R₇ and R₁₀ are each independently H or C₁ -C₄ alkyl;

R₈ is H, C₁ -C₄ alkyl or C₁ -C₄ haloalkyl;

Q is H or SO₂ R₁₁ ; and

R₁₁ is C₁ -C₄ alkyl or phenyl optionally substituted with one to threehalogen, NO₂, C₁ -C₄ alkoxy or C₁ -C₄ alkyl groups; or

the tautomers or the stereoisomers thereof.

It has now been found that the formula VII herbicidal agents may beprepared from readily available and easily obtainable starting materialsin a cost effective and efficient process of manufacture. In accordancewith the process of the invention the formula VII compound may beprepared by condensing an ester of formula IV with a-β-mercaptopropionicacid of formula V to form a thioenol compound of formula Ia;cyclodehydrating the formula Ia thioenol to form atetrahydrobenzothiopyran compound of formula Ib1; reacting the formulaIb1 compound with an oxylamine, H₂ NOR₈ or a salt thereof, to form thecorresponding oxime derivative of formula Ib2; aromatizing said formulaIb2 compound to give the dihydrobenzothiopyran intermediate of formulaIII; oxidizing the formula III intermediate to give the 1,1-dioxidecompound of formula VIII; hydrolyzing said formula VIII compound to givethe corresponding 6-carboxylic acid of formula IX; and reacting saidformula IX carboxylic acid with a 5-hydroxypyrazole of formula X in thepresence of a base and a dehydrating agent to give the6-(pyrazolylcarbonyl)dihydrobenzothiopyran product compound of formulaVIIa wherein Q is hydrogen; or, for compounds of formula VIIb wherein Qis SO₂ R₁₁, reacting the compound of formula VIIa with a sulfonylchloride, R₁₁ SO₂ Cl, to give the desired VIIb compound.

Optionally, the formula III intermediate may be prepared by reversingthe sequence of the oximation and aromatization steps. The completereaction sequence is shown in flow diagram V wherein R₁, R₂, R₃, R₄, R₅,R₆, R₇, R₈, R₉, R₁₀ and R₁₁ are described hereinabove. ##STR11##

The herbicidal agents of formula VIIa and formula VIIb and theirpreparation from intermediates of formula III are described in WO95/13275. The oxidation and hydrolysis steps described above may beaccomplished using conventional methods such as hydrogen peroxideoxidation and simple base hydrolysis techniques. The coupling of thehydroxypyrazole compound of formula X and the subsequent rearrangementto the desired compound formula VIIa may be performed using conventionalmethods such as those described in WO 95/13275, i.e. in the presence ofa base and a dehydrating agent. Similarly, the sulfonation of formulaVIIa with a sulfonyl chloride, R₁₁ SO₂ Cl, to give the desired formulaVIIb compound may be accomplished according to conventional methods.

For a more clear understanding of the invention, the following examplesare set forth below. These examples are merely illustrative and are notunderstood to limit the scope or underlying principles of the inventionin any way. Indeed, various modifications of the invention, in additionto those shown and described herein, will become apparent to thoseskilled in the art from the following examples and the foregoingdescription. Such modifications are also intended to fall within thescope of the appended claims.

The term ¹ NMR designates proton nuclear magnetic resonance.

EXAMPLE 1 Preparation of Ethyl4-β-carboxyrethylthio-2-methyl-1,3-cyclohexadiene-1-carboxylate##STR12## Method A

A solution of ethyl 2-methyl-4-oxo-2-cyclohexenecarboxylate (200 g, 1.1mole), β-mercaptopropionic acid (104.6 g, 0.99 mole) andp-toluenesulfonic acid hydrate (1.5 g, 0.0079 mole) in toluene is heatedat reflux temperatures, under N₂, using a Dean Stark trap for 18 hours,cooled and concentrated in vacuo to give a residue. The residue iscrystallized in 2:1 hexanes:ether to give the title product as a yellowsolid, 135 g (45% yield). A small sample was recrystallized from ethylacetate/hexane to give a pale yellow solid, mp 96°-97° C., identified by¹ HNMR and mass spectral analyses.

Method B

A solution of ethyl 2-methyl-4-oxo-2-cyclohexenecarboxylate (42.7 g,0.23 mole), trimethylborate (10.4 g, 0.10 mole), acetic anhydride (30.7g, 0.30 mole) and β-mercaptopropionic acid (24.2 g, 0.23 mole) intoluene is stirred at 15° C., treated with 20 drops of methanesulfonicacid and stirred at ambient temperatures for 18 hours. The resultantreaction mixture is partitioned between toluene and dilute aqueousammonia. The phases are separated and the organic phase is concentratedin vacuo to give an oil residue, 65.5 g, ¹ HNMR analysis of the residueshows the title product as the major component, also present are tolueneand starting cyclohexenecarboxylate.

EXAMPLE 2 Preparation of Ethyl5-methyl-4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyran-6-carboxylate##STR13##

A mixture ofethyl-4-β-carboxyethylthio-2-methyl-1,3-cyclohexadiene-1-carboxylate(121.3 g, 0.449 mole) in toluene is stirred at 20° C., treatedsequentially with 5.0 ml methanesulfonic acid and portionwise over a 5minute period with trifluoroacetic anhydride (94.3 g, 0.449 mole) andallowed to stir at ambient temperatures for 18 hours. The resultantreaction mixture is quenched with a 1:1 mixture of ethyl acetate andwater and stirred for 15 minutes. The phases are separated. The organicphase is washed with water and concentrated in vacuo to give a residue.Crystallization of the residue from isopropanol/heptane affords thetitle product as a yellow solid, 90.1 g, (79.5% yield), mp 99°-100° C.,identified by ¹ HNMR and mass spectral analyses.

EXAMPLE 3 Preparation of Ethyl5-methyl-4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyran-6-carboxylate##STR14##

A mixture of ethyl 2-methyl-4-oxo-2-cyclohexenecarboxylate (2.0 kg,91.2%, 10.98 moles), β-mercaptopropionic acid (1.165 kg, 10.98 moles),p-toluenesulfonic acid (ptsa) monohydrate (0.710 kg, 3.73 moles) andpyridine (0.304 kg, 3.84 moles) in toluene is heated to refluxtemperature, heated at reflux temperatures for 7 hours using a DeanStark trap for removal of water, allowed to cool to room temperatureover a 17 hour period, cooled to 5° C., treated with trifluoroaceticanhydride (TFAA) (2.306 kg, 10.98 moles) at 50°-12° C., treated withmethanesulfonic acid (0.053 kg, 0.55 moles), allowed to warm to roomtemperature, held at room temperature until reaction is complete by HPLCanalysis and quenched with water. The phases are separated. The organicphase is washed with water and distilled to remove the toluene. Theremaining pot residue is treated with isopropyl alcohol (1.89 kg),cooled to 45° C., treated with heptane (1.65 kg), and cooled to roomtemperature. The resultant mixture is filtered and the filtercake iswashed sequentially with a 1:1 isopropanol:heptane mixture (0.735 kg)and heptane (1.37 kg). The washed filtercake is dried in vacuo to givethe title product as a white crystalline solid, 0.931 kg (36% yield)98.4% purity, identified by HPLC analysis.

EXAMPLE 4 Preparation of Substituted4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyran-6-carboxylate ##STR15##

A mixture of substituted 4-oxo-2-cyclohexene-1-carboxylate (1.1 mole),β-mercaptopropionic acid (1.0 mole), p-toluenesulfonic acid hydrate(ptsa) (0.20 mole) and pyridine (0.2 mole) in toluene is heated atreflux temperatures using a Dean Stark (DS) trap for 3 hours. Theresultant solution is diluted with toluene, cooled to 10° C., treatedsequentially with methanesulfonic acid (0.0625 mole) and trifluoroaceticanhydride (TFAA) (1.0 mole) over a 5 minute period, stirred for 18 hours(the reaction temperature is allowed to rise to 21° C.), quenched withwater and stirred for 5 minutes. The phases are separated. The organicphase is washed with water and concentrated in vacuo to give a residue.Crystallization of the residue affords the title product.

Using essentially the same procedure described above, the compoundsshown below are obtained and identified by ¹ HNMR and mass spectralanalyses.

    ______________________________________                                          #STR16##                                                                    R.sub.1   R.sub.2                                                                              R.sub.3   mm ° C.                                                                       % yield                                     ______________________________________                                        C.sub.2 H.sub.5                                                                         CH.sub.3                                                                             H          99-100                                                                              56                                            CH.sub.3 CH.sub.3 H 138-140 16                                              ______________________________________                                    

EXAMPLE 5

Preparation of Ethyl5-methyl-4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyran-6-carboxylate,4-(O-methyloxime) ##STR17##

A mixture of ethyl5-methyl-4-oxo-2,3,7,8-tetra-hydro-4H-1-benzothiopyran-6-carboxylate(106 g, 0.42 mole), 151 g of 25-30% aqueous methoxylamine hydrochloride,50 ml of pyridine, 500 ml of toluene and 500 ml of ethanol is stirred atreflux temperature for 2 hours, cooled and concentrated in vacuo to givea residue. The residue is partitioned between ethyl acetate and diluteaqueous hydrochloric acid. The organic phase is separated, washed withwater and concentrated in vacuo to give a second residue. This residueis crystallized from hexanes to give the title product as a white solid,37.6 g (32% yield), mp 65°-67° C., identified by ¹ HNMR, and massspectral analyses.

EXAMPLE 6 Preparation of Ethyl5-methyl-4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyran-6-carboxylate,4-oxime ##STR18##

A mixture of ethyl 5-methyl-4-oxo-23,7,8-tetrahydro-4H-1-benzothiopyran-6-carboxylate (156 g, 0.619 mole),hydroxylamine hydrochloride (43 g, 0.619 mole), 100 ml of pyridine in1.0 L of absolute ethanol is stirred at reflux temperature for 18 hours,cooled and concentrated in vacuo to give a residue. The residue ispartitioned between dilute aqueous NaCl and an ethyl acetate/methanolmixture. The resultant phase mixture is acidified to pH 1 withconcentrated hydrochloric acid. After mixing, the phases are separatedand the organic phase is concentrated in vacuo to give a second residue.This residue is slurried in diethyl ether and filtered to afford thetitle product as an off-white solid, 110 g (66.5% yield) mp 139°-142°C., identified by ¹ HNMR and mass spectral analyses.

EXAMPLE 7 Preparation of Ethyl2,3-dihydro-5-methyl-4-oxo-4H-1-benzothiopyran-6-carboxyrlate,4-(O-methyloxime) ##STR19## Method A

A solution of ethyl5-methyl-4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyrano-6-carboxylate,4-(0-methyloxime) (100 g, 0.356 mole) in a 1:1 mixture of methylenechloride and chloroform is stirred at 5° C., treated dropwise with asolution of bromine (56.5 g, 0.353 mole) in methylene chloride over a 30minute period, stirred at room temperature for 16 hours and heated atreflux temperature for 5 hours. (The liberated hydrogen bromide gas isscrubbed during the entire procedure.) The reaction mixture is cooledand concentrated in vacuo to give a residue. The residue is partitionedbetween ethyl acetate and dilute aqueous ammonia. The phases areseparated and the organic phase is washed with dilute aqueous NaHSO₃ andconcentrated in vacuo to afford an oil residue. ¹ HNMR analysis of theresidue shows the title product as the major component.

Method B

A mixture of ethyl5-methyl-4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyran-6-carboxylate,4-(0-methyloxime) (2.8 g, 0.01 mole), 7 ml of acetic acid and 0.7 g of50% aqueous hydrogen peroxide is stirred at room temperature overnight,treated, with cooling, with 0.82 g acetyl chloride and stirred atambient temperatures for 1 hour. Thin layer chromatographic analysisshows the title product as the major component.

EXAMPLE 8 Preparation of Ethyl2,3-dihydro-5-methyl-4-oxo-4H-1-benzathiopyran-6-carboxylate ##STR20##

A mixture of ethyl5-methyl-4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyrano-6-carboxylate (25g, 0.099 mole) and 7 g of 5% Pd/C catalyst in 100 ml of cymene is heatedat ref lux temperature (about 175° C.) for 24 hours, cooled to 80° C.and filtered. The catalyst filtercake is washed with toluene. Thefiltrates are combined and concentrated in vacuo to afford the titleproduct, 25.9 g, 90% purity by ¹ HNMR analysis (94% yield).

What is claimed is:
 1. A compound of formula I ##STR21## wherein R₁ andR₂ are each independently C₁ -C₄ alkyl;W₁ is --SCR₄ R₅ CR₆ R₇ COOH; W₂is H or W₁ and W₂ may together with the carbons to which they areattached form a ring in which W₁ and W₂ represent ##STR22## Z is O orNOR₈ R₃, R₄, R₅, R₆ and R₇ are each independently H or C₁ -C₄ alkyl; andR₈ is H, C₁ -C₄ alkyl or C₁ -C₄ haloalkyl or when Z is NOR₈, thestereoisomers thereof.
 2. The compound according to claim 1 wherein R₃,R₄, R₅, R₆ and R₇ are H.
 3. The compound according to claim 2 wherein R₁is methyl or ethyl.
 4. The compound according to claim 1 wherein Z isNOR₈.
 5. The compound according to claim 2:ethyl5-methyl-4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyran-6-carboxylate;ethyl5-methyl-4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyran-6-carboxylate,4-oxime; ethyl5-methyl-4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyran-6-carboxylate,4-(0-methyloxime); or ethyl4-β-carboxyethylthio-2-methyl-1,3-cyclohexadiene-1-carboxylate.
 6. Aprocess for the preparation of a compound of formula I ##STR23## whereinR₁ and R₂ are each independently C₁ -C₄ alkyl;W₁ is --SCR₄ R₅ CR₆ R₇COOH; W₂ is H or W₁ and W₂ may together with the carbons to which theyare attached form a ring in which W₁ and W₂ represent ##STR24## R₃, R₄,R₅, R₆ and R₇ are each independently H or C₁ -C₄ alkyl; Z is O or NOR₈ ;and R₈ is H, C₁ -C₄ alkyl or C₁ -C₄ haloalkyl; or when Z is NOR₈, thestereoisomers thereof which process comprises condensing a compound offormula IV ##STR25## with a β-mercaptopropionic acid of formula V##STR26## to give a thioenol compound of formula Ia ##STR27## and in thecase wherein W₁ and W₂ form a ring further cyclodehydrating saidthioenol compound of formula Ia to give the tetrahydrobenzothiopyrancompound of formula Ib1, wherein Z is O and, in the case where Z isNOR₈, further reacting said tetrahydrobenzothiopyran compound with anoxylamine H₂ NOR₈ or a salt thereof to give the compound of formula Ib2wherein Z is NOR₈.
 7. The process according to claim 6 wherein thecondensation is carried out in the presence of a condensation solventand an acid catalyst.
 8. The process according to claim 7 wherein thecondensation is carried out in the presence of a dehydrating agent orthe azeotropic removal of water.
 9. The process according to claim 7wherein the condensation solvent is selected from the group consistingof toluene, benzene, halobenzene and xylene.
 10. The process accordingto claim 7 wherein the acid catalyst is selected from the groupconsisting of sulfuric acid, methanesulfonic acid, p-toluenesulfonicacid, pyridinium p-toluenesulfonate, pyridinium methanesulfonate andboron trifluoride.
 11. The process according to claim 10 wherein theacid catalyst is pyridinium p-toluenesulfonate or pyridiniummethanesulfonate.
 12. The process according to claim 8 wherein thedehydrating agent is selected from the group consisting of aceticanhydride, triethyl orthoformate, trimethylborate and mixtures thereof.13. The process according to claim 6 wherein the cyclodehydration iscarried out in the presence of a cyclodehydration solvent and an acidcatalyst.
 14. The process according to claim 13 wherein thecyclodehydration solvent is selected from the group consisting oftoluene, benzene, halobenzene and xylene.
 15. A process for thepreparation of a compound of formula III ##STR28## wherein R₁ and R₂ areC₁ -C₄ alkyl;R₃, R₄, R₅, R₆ and R₇ are each independently H or C₁ -C₄alkyl; and R₈ is H, C₁ -C₄ alkyl or C₁ -C₄ haloalkyl; or thestereoisomers thereof which process comprises the following steps:a)condensing an ester of formula IV ##STR29## with a β-mercaptopropionicacid of formula V ##STR30## to give a thioenol intermediate compound offormula Ia ##STR31## b) cyclodehydrating said thioenol intermediate togive a 4-oxo-tetrahydrobenzothiopyran intermediate compound of formulaIb1 ##STR32## c) aromatizing said 4-oxo-tetrahydrobenzothiopyranintermediate of step (b) to give the 4-oxo-dihydrobenzothiopyranintermediate of formula VI ##STR33## and reacting said4-oxo-dihydrobenzothiopyran intermediate with an oxylamine, H₂ NOR₈ or asalt thereof; or reacting said 4-oxo-tetrahydrobenzothiopyranintermediate of step (b) with an oxylamine H₂ NOR₈ or a salt thereof togive the 4-oximino-tetrahydrobenzothiopyran intermediate compound offormula Ib2 ##STR34## and aromatizing said4-oximino-tetrahydrobenzothiopyran intermediate to give the productcompound of formula III ##STR35## wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇ andR₈ are defined hereinabove.
 16. The process according to claim 15wherein the condensation is carried out in the presence of acondensation solvent and acid catalyst.
 17. The process according toclaim 16 wherein the condensation is carried out in the presence of adehydrating agent or the azeotropic removal of water.
 18. The processaccording to claim 16 wherein the condensation solvent is selected fromthe group consisting of toluene, benzene, halobenzene and xylene. 19.The process according to claim 16 wherein the acid catalyst is selectedfrom the group consisting of sulfuric acid, methanesulfonic acid,p-toluenesulfonic acid, pyridinium p-toluenesulfonate, pyridiniummethanesulfonate, and boron trifluoride.
 20. The process according toclaim 19 wherein the acid catalyst is pyridinium p-toluenesulfonate orpyridinium methanesulfonate.
 21. The process according to claim 15wherein the cyclodehydration is carried out in the presence of acyclodehydration solvent and a dehydrating agent and optionally in thepresence of an acid catalyst.
 22. The process according to claim 21wherein the cyclodehydration solvent is selected from the groupconsisting of toluene, benzene, halobenzene and xylene.
 23. The processaccording to claim 21 wherein the dehydrating agent is selected from thegroup consisting of acetic anhydride, trifluoroacetic anhydride,phthaloyl chloride, trifluoroacetyl chloride and acetyl chloride.
 24. Aprocess for the preparation of a herbicidal compound of formula VII##STR36## wherein R₂ and R₉ are each independently C₁ -C₄ alkyl;R₃, R₄,R₅, R₆, R₇ and R₁₀ are each independently H or C₁ -C₄ alkyl; R₈ is H, C₁-C₄ alkyl or C₁ -C₄ haloalkyl; Q is H or SO₂ R₁₁ ; and R₁₁ is C₁ -C₄alkyl or phenyl optionally substituted with one to three halogen, NO₂,C₁ -C₄ alkyl, or C₁ -C₄ alkoxy groups; orthe stereoisomers or thetautomers thereof which process comprises the following steps: a)condensing an ester of formula IV ##STR37## with a β-mercaptopropionicacid of formula V ##STR38## to give a thioenol intermediate compound offormula Ia ##STR39## b) cyclodehydrating said thioenol intermediate togive a 4-oxo-tetrahydrobenzothiopyran intermediate compound of formulaIb1 ##STR40## c) reacting said 4-oxo-tetrahydrobenzothiopyran with anoxylamine H₂ NOR₈, or a salt thereof to give the4-oximino-tetrahydrobenzothiopyran intermediate compound of formula Ib2##STR41## d) aromatizing said 4-oximino-tetrahydrobenzothiopyranintermediate to give a 4-oximino-dihydrobenzothiopyran intermediatecompound of formula III ##STR42## e) oxidizing saiddihydrobenzothiopyran intermediate to give a1,1-dioxo-dihydrobenzothiopyran intermediate compound of formula VIII##STR43## f) hydrolyzing said formula VIII intermediate to give thecorresponding 1,1-dioxo-4-oximino-dihydrobenzothiopyran-6-carboxylicacid of formula IX ##STR44## g) reacting saiddihydrobenzothiopyran-6-carboxylic acid intermediate with a5-hydroxypyrazole of formula X ##STR45## in the presence of adehydrating agent-and a base to give the desireddihydro-6-[(5-hydroxypyrazol-4-yl)carbonyl]benzothiopyran herbicidalcompound of formula VII wherein Q is H (VIIa) ##STR46## and optionally(VIIa) h) reacting saiddihydro-6-[(5-hydroxypyrazol-4-yl)carbonyl]benzothiopyran compound witha sulfonyl chloride, R₁₁ SO₂ Cl, to give the product herbicidal compoundof formula VII wherein Q is SO₂ R₁₁ (VIIb) ##STR47## and wherein R₂, R₃,R₄, R₅, R₆, R₇, R₈, R₉ R₁₀, and R₁₁ are defined hereinabove.
 25. Aprocess for the purification and isolation of a compound of formula Ib1##STR48## wherein R₁ and R₂ are each independently C₁ -C₄ alkyl; andR₃,R₄, R₅, R₆ and R₇ are each independently H or C₁ -C₄ alkylwhich processcomprises treating said compound with a solvent mixture of isopropanoland heptane to give a resultant mixture containing a crystalline solidand filtering the resultant mixture.
 26. The process according to claim25 wherein the solvent mixture is about 1:1 volume/volumeisopropanol:heptane.
 27. The process according to claim 25 wherein R₃,R₄, R₅, R₆ and R₇ are H.
 28. The process according to claim 25 whereinR₁ is methyl or ethyl.
 29. The process according to claim 28 for thepurification and isolation of the compound ethyl5-methyl-4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyran-6-carboxylate.